The HgCdTe electron avalanche photodiode |
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Authors: | J Beck C Wan M Kinch J Robinson P Mitra R Scritchfield F Ma J Campbell |
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Affiliation: | (1) DRS Infrared Technologies, LP, 75374 Dallas, TX;(2) Microelectronics Research Center, University of Texas, 78712 Austin, TX |
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Abstract: | Electron injection avalanche photodiodes in short-wave infrared (SWIR) to long-wave infrared (LWIR) HgCdTe show gain and excess
noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD)
with “ideal” APD characteristics including near noiseless gain. This paper reports results obtained on long-, mid-, and short-wave
cutoff infrared Hg1−xCdxTe EAPDs (10 μm, 5 μm, and 2.2 μm) that use a cylindrical “p-around-n” front side illuminated n+/n-/p geometry that favors
electron injection into the gain region. These devices are characterized by a uniform, exponential, gain voltage characteristic
that is consistent with a hole-to-electron ionization coefficient ratio, k=αh/αe, of zero. Gains of greater than 1,000 have been measured in MWIR EAPDS without any sign of avalanche breakdown. Excess noise
measurements on midwave infrared (MWIR) and SWIR EAPDs show a gain independent excess noise factor at high gains that has
a limiting value less than 2. At 77 K, 4.3-μm cutoff devices show excess noise factors of close to unity out to gains of 1,000.
A noise equivalent input of 7.5 photons at a 10-ns pulsed signal gain of 964 measured on an MWIR APD at 77 K provides an indication
of the capability of this new device. The excess noise factor at room temperature on SWIR EAPDs, while still consistent with
the k=0 operation, approaches a gain independent limiting value of just under 2 because of electron-phonon interactions expected
at room temperature. The k=0 operation is explained by the band structure of the HgCdTe. Monte Carlo modeling based on the
band structure and scattering models for HgCdTe predict the measured gain and excess noise behavior. |
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Keywords: | Infrared avalanche photodiode APD mercury cadmium telluride HgCdTe avalanche gain bandwidth ionization coefficient excess noise factor Monte Carlo simulations |
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